The present invention relates to a feed mechanism of a fetal monitor printer for feeding zigzag paper from either side of a zigzag paper pack.
Corometrics Medical Systems has sold a Model 115 fetal monitor printer that is designed to only bottom feed zigzag paper.
This printer has a housing and a door pivoted to the housing. In the door is a drive roller and a paper retention pocket. A print head with thermal fingers is provided on the housing, opposite the drive roller when the door is closed. A zigzag paper pack is inserted into the pocket when the door is open. An optical sensor is provided for detecting the end of paper of the zigzag paper pack.
In practice, the bottom sheet of the zigzag paper pack is positioned to stick out of the paper retention pocket when the pack is inserted into the pocket. The paper thus extends over the drive roller. When the door is closed and the printer operated, the drive roller will feed the paper out of the pocket from the underside of the paper pack. The print head is in position opposite the drive roller to commence printing onto the paper with its thermal fingers.
Due to the nature of the zigzag paper pack, the pack leans against a sidewall of the paper retention pocket with whichever side of the pack is not being pulled by the drive roller.
It is possible that the zigzag paper pack is improperly positioned in the pocket, because of operator error. In the rush of delivery room activity, for instance, the zigzag paper pack may be inadvertently inserted into the pocket so that its top sheet sticks out over the drive roller, rather than its bottom sheet from underneath the pack. If this occurs, subsequent operation of the printer may lead to lost data and machine stoppage, because the pack eventually becomes thin and light enough to be pulled out all at once from the pocket.
U.S. Pat. No. 4,748,457 discloses a recording device in which zigzag or Z fold paper is loaded into a tray located within the device when the door of the device is open. The door has a trench with side walls, between which a sheet of the paper becomes trapped by a plate when the door is closed so as to ensure that it is properly positioned for operation. When the door closes, the end sheet of the paper is pressed against a thermal print head by a drive roller. A latch mechanism keeps the door releasably closed by means of a pivoted lever which has an end projection that is spring biased into a receiving groove when the door closes. The drive roller is belt driven by a motor. Two belts are provided which have an end wrapped around gear wheels on a pivot shaft of the door for transmitting rotary motion. The paper pack lies horizontally and does not stand upright in the tray.
U.S. Pat. No. 4,218,031 discloses a zigzag paper pack loaded into a V-shaped trough compartment of a feed mechanism. A drive roller with pins pulls the paper out from the pack out of the compartment in a generally horizontal direction. Nothing guides the paper to enable pulling the paper from either side of the pack without mishap.
U.S. Pat. Nos. 4,139,855; 4,296,420; 4,348,118; 4,567,492 and 4,631,552 all disclose zigzag paper feed mechanisms in which the zigzag paper pack is laid down horizontally for feeding from its top only, rather than standing upright vertically for feeding from either side.
U.S. Pat. Nos. 2,718,450 and 3,216,021 disclose feed mechanisms for feeding paper on a paper roll in either the clockwise or counterclockwise directions, but always by pulling on the outside sheet of the paper roll. No zigzag paper is used and no paper retention pocket in a door is utilized. Also, no biasing means is present between the paper roll and the drive roller.